peritoneum vs omentum

peritoneum and omentum both are nouns.

Word	Noun	Adjective	Verb	Adverb
peritoneum	Yes	No	No	No
omentum	Yes	No	No	No

As nouns, omentum is a hyponym of peritoneum; that is, omentum is a word with a more specific, narrower meaning than peritoneum:

peritoneum: a transparent membrane that lines the abdominal cavity in mammals and covers most of the viscera
omentum: a fold of peritoneum supporting the viscera

Other hyponyms of peritoneum include mesentery.

peritoneum (noun)	omentum (noun)
a transparent membrane that lines the abdominal cavity in mammals and covers most of the viscera	a fold of peritoneum supporting the viscera